Die



Feb. 7, 1967 E, SEN A; 3,302,239

DIE

2 Sheets-Sheet 1 INVENTOR VANCE EVAN SENEGAL Filed May 24 1965 ATTORNEYFeb. 7, 1967 v. E. SENEGAL 3,302,239

DIE

Filed May 24, 1965 2 Sheets-Sheet 2 INVENTOR VANCE EVAN SENEGAL ATTORNEYUnited States Patent 3,302,239 DIE Vance Evan Senecal, Wilmington, Del,assignor to E. I. du Pont de N emours and Company, Wilmington, Del.

Filed May 24, 1963, Ser. No. 283,018 4 Claims. (Cl. 1812) This inventionrelates to an extrusion coating die for applying a coating to a movingweb. More particularly it relates to a low pressure extrusion coatingdie with a permanently shaped flow distribution channel.

Photographic films and papers usually have a sheet support and amultiplicity of layers. In the case of blackand-white films, not as manylayers are required as for multicolor films. In the former films,however, it is common to coat a gelatino-silver halide emulsion onto afilm base and then to coat the emulsion layer with a non-photographicaqueous gelatin solution to provide an antiabrasion layer. In colorfilms, there is usually a separate layer for recording each of theprimary colors, and yielding a dye image in addition to tfilter andantiabrasion layers. All of the above layers are usually formed byseparate coating operations. The various layers in theses multiplayerphotographic elements, particularly in the case of color films, shouldbe of uniform thickness and free from defects.

In black-and-white films the variation in coating weight, ideally,should not exceed i2.0%, and in multicolor films, i1.0%. In order tocoat a highly viscous photographic emulsion having a low fluid contentat high speeds, emulsions are extruded through a die at elevatedpressures. Dies suitable for this purpose usual-1y comprise an internalsupply chamber and an orifice formed by two lips co-extensive with saidchamber. In order to deposit the desired amount of emulsion per unit ofsurface at coating speeds of 80 to 400 feet per minute, the orifice mustbe precisely adjusted and the lips rigid so that the width of theorifice throughout its entire length can be maintained within precisenarrow limits. This is because for ideal or so-ca-lled Newtonian fluidsthe coating weight varies as the third power of the width between thelips.

Since fluid photographic emulsions are non-Newtonian in character, thecoating weight of the emulsion layer may vary as much as the 4th or thpower of the gap or width dimension variation between the die lips. Ithas been found that, even where the die and lips are rigid, it isdifficult to maintain the transverse coating weight uniform within theabove limits. This is due in part to the deflecton of the die lipsduring the high pressure extrusion thereby giving a non-uniform coatingweight profile.

Various types of dies have been proposed in order to provide uniformcoatings but uniform flow distribution throughout dies of considerablelength is difiicult to attain and improper distribution causes defectsin the form of streaks.

The use of an internally braced die as disclosed in assignees SenecalUS. application Ser. No. 128,775 filed Aug. 2, 1961, now Patent No.3,151,356, has reduced the non-uniformity of coating weight by reducingthe deflection of the die lips, but the braces can cause flow patternsor streaks in the coated web.

An object of this invention is to provide an improved extrusion die. Afurther object is to provide an extrusion die which will give a uniformcoating under conditions of elevated fluid pressures. Another object isto provide such a die which will give smooth, uniform, wide coatingsdevoid of streaks and other coatings defects. A further object is toprovide a simple and dependable extrusion die. A further object is toprovide a die hav- 3,302,239 Patented Feb. 7, 1967 ing improved flowdistribution. A further object is a die which provides the requiredfluid distribution at reduced internal pressures, i.e., not more than 40pounds per square inch. A still further object is to provide a simpledie that can be readily assembled and is useful in applying one coatingor two coatings simultaneously to a web. Still other objects will beapparent from the following description of the invention.

According to the present invention, there is provided an extrusion diefor controlling the flow to fluid along diverging paths from an inlet toand through a narrow slot outlet comprising:

(a) A body member having at least one inlet and an outlet terminating ina side surface of the body member, a portion of said surface definingone surface of the slot outlet,

(b) A fluid control plate on a side surface, the inner surface of whichplate has a series of interconnected depressed chamber areas formingwith said surface (1) A centrally disposed inlet area,

' (2) A transverse supply chamber,

(3) A transverse real restricted passage, and

(4) A sec-0nd transverse cross-flow chamber that provides another flowcontrol passage adjacent the slot outlet and communicates with said slotoutlet.

The chamber area forming the transverse rear restricted passage can beof lesser or greater depth than the chamber area of the cross-flowchamber.

At least one of the leading and trailing edges of the transverse rearrestricted passage is curved from a central point to the lateral edge sothat integral units of emulsion passing from the inlet through thesupply chamber and traveling the shortest path to the cross-flow chambermust travel a longer distance through the restricted passage tocompensate for diiferences in pressure drop. The length of thetransverse rear restricted passage in the direction of fluid flow isvaried along diverging paths of fluid flow from the centrally disposedfluid opening to the slot outlet to equate total pressure drops alongeach of said paths.

In the preferred die, shown in the drawings, the die body iswedge-shaped and has a control plate on each surface. If desired, eachcontrol plate can be provided with a pressure measuring and controllingdevice mounted adjacent to and in communication with the fluid supplychamber. Also, if desired, the body and/ or plate can be provide withpassages and fittings so that the heat exchange fluid can be circulatedtherethrough to control the temperature of the body or plate.

The invention will now be described with reference to the accompanyingdrawings in which:

FIG. 1 is a vertical cross-section of the die taken along the line 11 of'FIG. 2 except that the pressure transducer and bolts, respectively, arenot shown in the lower and upper plates.

FIG. 2 is a plan view of one of the plate members showing the locationof the flow distribution chambers or recesses in relation to the lips ofthe die;

FIG. 3 is an isometric view of the inner surface of the control plateshowing the various dimension symbols used in the mathematicalcomputation; and

FIG. 4 is an enlarged, modified vertical sectional view of the leftportion of FIG. 1 and showing various dimension symbols.

Referring now to the drawings, wherein the same reference numerals referto the same parts in the several views, the extrusion die of thisinvention comprises a In the inner surface of each plate andcommunicating with a fluid inlet area is a recessed, transverse supplychamber 5. Spaced therefrom is a second recessed transverse cross-flowchamber 6, the bottom wall 7 of which at its trailing edge slopesinwardly toward the coacting slanting surface of the body member untilit meets a slot orifice-defining surface 8, which is preferably parallelto said surface for a short distance. Between the supply chamber and thecross-flow chamber formed with the surface of the body and the platethere is a recessed, rear, restricted fluid distribution passage 9 ofless depth than supply chamber 5.

Either the trailing edge 10, leading edge 11, or both, of the rear,restrictive fluid distribution passage are shaped according to amathematical calculation so that the integral units of emulsion passingfrom the inlet through the supply chamber in traveling the shortest pathto the rear restrictive passage must travel a longer length through therestricted distribution passage to compensate for the differences inpressure drop.

The shape of the edge is calculated on an approximate solution of theequations of motion for a Newtonian fluid. Referring to FIGURE 3, Pequals the pressure at the inlet to the supply chamber; P(x) equals thepressure at a perpendicular distance x from the center of the die, Lequals the length of the supply chamber from the center of the die andequals the pressure gradient in a channel of the same shape as the fluidsupply chamber but without distributing fluidallowance being made,however for fluid removal en route. The proper design of the shapededge, the leading edge 11 in this case, requires that the pressure atthe trailing edge of the rear restrictive passage 9 be uniform along theedge. The critical step in the design is the calculation of the supplychamber pressure at various points along the leading edge. It can beshown mathematicaly and experimentaly that as the ratio of the width ofthe feeding chamber to the length of the chamber becomes small, thepressure in the chamber at position x The shape of the leading edge isdetermined then by specifying that the pressure at the trailing edge ofthe rear restrictive passage is constant, thus obtains the length ofpassage Y in a particular location as where b equals the depth of therear restrictive passage and C is a function of the geometry of thesupply chamber.

Use of this computation is strictly valid only when the fluid isNewtonian in both the supply chamber and the rear restrictive passageand the ratio of the width of the supply chamber to its length tendstoward zero, but it has been found experimentally that any deviation issmall and can be compensated for by the cross flow chamber.

In a die where the depth of the supply chamber was 0.313 inch, the widthof the chamber is 1.000 inch, and the depth of the rear restrictivepassage b is 0.120 inch the length of the rear restrictive passage isequal to 0.4 68

Using this die it was found that the coating weight uniformity hasvariations below i2% over 9095% of the film width and below -:1% over80-85% of the width.

The cover plates are fastened to the wedge-shaped member by a pluralityof machine screws 12 which extend through the control plates and havethreaded engagement with threaded holes (not numbered) in the bodymember. If desired, as shown in FIG. 1, the heads of these screws canfit in recesses 13 in the plates.

Each plate is preferably provided with a lateral socket 14 opposite thefluid supply chamber and having communication therewith through passages15. A pressuresensitive device, e.g., a pressure transducer 16, isplaced in the socket and is fixed in place by a suitale guide sleeve 17and held in place by suitable flanges 18, which are held in place bymeans of screws 19. A lateral pipe 20 extends through the cap and isconnected to the transducer. The pipe connects with a suitable controldevice so that the fluid pressure in the fluid supply chamber can becontrolled and determined.

Coacting with each fluid inlet passage 3 there is a pipe sealing flange21 which is fastened to the upper surface of the body member. Pipe 22fitted into the flange connects to a source of fluid material to beextruded. The source for one supply chamber can be different from thatof the other chamber. The body member and/or each plate or both platescan be provided with channels or passages 23 for circulation of aheat-exchange liquid.

As shown in FIG. 1 of the drawing, the bottom edges of each platepreferably converge at or near the apex of the body member so that thesheets of material being extruded meet at or near the orifice. In thisway a composite sheet can be formed from the two extruded layers as theycome into surface contact. The bottom of each of the plates can be ofthe same pointed shape or they can be different, as shown in FIG. 1 ofthe drawings.

The wedge shaped body may come to a knife-edge or sharp point or it maybe truncated slightly to form, for example, a narrow, fiat edge, e.g.,about 0.002 inch in width.

Referring to FIG. 4, the use of low internal pressure provides forbetter coating geometry. With very little deflection problem the lip tipangles Q can be reduced to approximately 30 in both the plates and thewedge piece. These small angles permit closer access to the coatingroller 24 and shorten the distance between the end of the orifice andthe surface of the web being coated, thereby minimizing susceptibilityto coating disturbances. The use of a coating roller with a smalldiameter, i.e., /2 inch in conjunction with the low lip tip angle alsopermits said distance or extrudate length to be described.

The extrudate angle A or the angle formed between the die slot fromwhich the emulsion emerges and a line drawn from the die lips to thecoating roll tangent also has an effect on the uniformity of thecoating. An angle of or greater with as short an extrudate 2: aspossible is the ideal condition. It was found that with an angle of andan extrudate of 0.150 inch the uniformity of the coated emulsion waswithin the desired limits.

In assembling the device the plate members are put in place and fasteneddown with the screws 12. A gasket (not shown) should be inserted aroundthe periphery or outside edges of the plates to seal the chambers.

The control plates and wedge-shaped member can be made of any strongmetal or metal alloy. The plates and wedge-shaped member, for example,can be made of cast iron, stainless steel, die steel, including vanadiumsteel, titanium, brass or bronze. For example, when coating aphotographic emulsion with an 0.012-inch lip opening to control coatingweights within 10.5 to 1% across the web, all interior surfacesincluding mating surfaces and the die lips must be highly polished towithin a dimensional accuracy :20 micro-inches. The particular metalused will depend on the corrosive characteristics of the material beingcoated. The various screws, bolts, etc. can be made of steel, stainlesssteel, titanium or other suitable metal or metal alloy.

In operation, when coating, for example, a viscous, aqueous photographicsilver halide gelatin emulsion and an aqueous gelatin solution to forman antiabrasion layer, the extrusion coating die is placed in positionfor coating a suitable web. In FIG. 1, the extrusion coating die isshown in position relative to the coating roll supporting the web to becoated. In normal coating position, the center line of the emulsion flowpath should be directed up at an angle of 35 to the horizontal andapproximately tangent to the coating roll surface. The length of theunsupported region of flow for the composite sheet of silver halideemulsion layer and antiabrasion layer where it is being drawn down fromthe plane of the tips of the lips on the control plates 4 to the pointof contact with the web on the coating roll should not exceed 0.300 inchin the direction of web travel. In the arrangement, a continuous sheetof film or paper 25 from a source (not shown) passes around coatingroller 24 and to a suitable drying Zone and thence to a windup apparatus(all not shown).

In using the extrusion die of this invention, two thin wide layers ofviscous materials are simultaneously extruded under pressure and broughtinto surface contact at or near the orifice, then applied to the surfaceof a continuous web moving at a speed greater than the speed ofextrusion. The layers, as they leave the orifice, can be about .00025 to.014 inch in thickness and when one layer is used as a sublayer orprotective layer for the main layer, in general, it will be to /2 thethickness of the former. By having the web moving at a rate of speedfaster than the speed of extrusion, one can obtain a drawdown of theextruded film 1 to 2.00 times in thickness at coating speeds greaterthan 80 feet per minute, particularly with viscous liquids having aviscosity of 2000 to 50,000 centipoises. Pressures of to 40 pounds persquare inch can be used. If desired, a single layer of a desired coatingmaterial may also be coated by using only one side of the novel coatingdie.

In an exemplary procedure of coating a single layer, a silver halideemulsion was made, extruded, and coated onto a cellulose acetate filmbase as follows:

A dilute aqueous photographic emulsion containing about 5.98% silverhalide and about 10% gelatin by weight was concentrated by heating it ina climbing film evaporator and the temperature adjusted to about 107 P.where the viscosity was about 5 000 centipoises. The silver halideemulsion coating solution was fed from a pressurized chamber into oneinlet passage 3 of the dual extrusion coating die of this invention. Theflow rate was adjusted so that the emulsion was applied at the rate ofapproximately 60 mg. silver halide per square decimeter.

The die lips were placed above a 4 inch diameter coating roller so thatthe draw-down span between the web and the bottom edge of the plate onthe left side was 0.150 inch. The pressure in the coating chamber washeld at 45 mm. mercury absolute and the coating speed was 252 feet perminute. After coating, the emulsion was dried, and had satisfactoryphotographic quality. The layer of emulsion had good adherence to thebase and the layer was uniform in thickness throughout its areaindicating a uniform transverse coating weight profile across the widthof the web.

The extrusion die of the invention is particularly useful insimultaneously extruding (a) a thin layer of an aqueous dispersion oflight-sensitive silver halide in a natural or synthetic water-permeablecolloid and (b) a thin protective layer of a water-permeable colloidcontaining an antistatic agent, or (c) an antihalation layer from anaqueous dipsersion or solution of an antihalation pigment or dye in awater-permeable colloid binding agent and then applying the compositelayer to the surface of a moving web of film or paper. Alternatively,two different aqueous dispersions of silver halides in a water-permeablemacromolecular organic colloid can be extruded simultaneously and thecomposite layer coated onto a continuous moving web. The above twodifferent dispersions may contain color formers or filter dyes and maybe two of the record and/orauxiliary layers of a multilayer film forcolor photography. An important feature of the invention is that thenovel coating die can just as easily be used to coat single layerproducts.

Various kinds of liquid or liquefied materials can be extruded by theapparatus of this invention. Among such materials are film-formingpolymers including polyethylene, polyvinyl chloride, poly(vinylchloride00 vinyl acetate), polymethyl methacrylate, polystyrene, polyethyleneterephthalate; regenerated cellulose, cellulose acetate, cellulosepropionate, cellulose acetate butyrate and ethyl cellulose; rubberhydrochloride, etc. These materials can be extruded in the form of anaqueous dispersion, solution in a solvent, or in molten or liquefiedform. The apparatus is especially useful in coating gelatine-silverhalide emulsions, and other dispersions of finely divided materials inwater-permeable colloids.

When the material being extruded has to be held at a certaintemperature, a heat-exchange fluid, e.g., water, diphenyl oxide,chlorinated biphenyl, chlorinated naphthalene and parafiin hydrocarbonoils, maintained at the requisite temperature, is passed through thecirculation passages in the wedge-shaped member and the plate members.

Antiabrasion coatings, such as those used to coat X-ray sensitive silverhalide emulsions are effective in thicknesses as low as thirtymillionths of an inch. Yet, such exceedingly thin layers are diflicultto extrude or coat in the form of uniform wide layers. By using theextrusion die of this invention, such exceedingly thin layers can bereadily extruded and coated onto webs over long periods of time. Byextruding one extremely thin silver halide emulsion layer in contactwith a thick emulsion layer, the composite films or layers can bestretched during the coating operation, whereas the extremely thin layerwould be too fragile to be stretched or drawn down separately.

The apparatus of this invention has the advantage that it is simple indesign but dependable in operation. It enables one to extrude acomposition onto a rapidly moving web with uniform distributionthroughout the thickness and width of the layer and without coatingstreaks. A further advantage of the invention is that the apparatusenables one to provide an extruded composite film having a uniformcoating weight profile across the width of the coating or layer. A stillfurther advantage of the die of this invention is that it has a fewsimple parts which can be readily assembled and quickly adjusted to givea coating of uniform profile.

The photographic films and papers obtainable by use of the extrusion dieof this invention, moreover, have improved characteristics. Multilayercol-or films having extremely thin filter, light-absorbing barrier andother layers contiguous with or adjacent to a silver halide emulsionlayer or layers, antihalation layers, etc., have improved resolutionover films having thicker layers obtainable by conventional ooatingmethods.

I claim:

1. An extrusion die for controlling the flow of fluid along divergingpaths from an inlet to and through a narrow slot outlet comprising:

(a) a body member having at least one inlet and an outlet terminating ina side surface of the body member, a portion of said surface definingone surface of the slot out-let,

(b) a fluid control plate on a side surface, the inner surface of whichplate has a series of interconnected depressed chamber areas formingwith said side surface (1) a centrally disposed inlet area, (2) anunobstructed transverse supply chamber,

7 8 (3) a transverse unobstructed rear restricted pas- 3. An extrusiondie according to claim 1 where the sage, and chamber are-a forming therestricted passage is of greater (4) an unobstructed second transversecross-flow depth than the chamber area of the cross-flow chamber.chamber that provides another flow control pas- 4. An extrusion dieaccording to claim 1 wherein said sage adjacent the slot outlet andcommunicates 5 body member is wedge shaped and the side surface of thewith said slot outlet, the length of the transverse body member is aslanting surface. rear restricted passage in the direction of fluid flowfrom said centrally disposed inlet area to References Cited y theExamine! the slot outlet being varied along diverging paths UNITEDSTATES PATENTS of fluid flow from said inlet area to said slot outlet 10to equate total pressure drops along each of said at paths, the shape ofthe curved leading edge of 2932855 4/1960 Bartlett-e121 18-15 X saidrestricted passage being determined by 10/1962 Reifenhauser' 18 12vmaintaining the pressure at the trailing edge of 3118179 1/1964 Bonner18 12 the rear restricted passage at all points so that 15 315135610/1964 Senecal 1812 at a par icular poin in the leading edge of the3197815 8/1965 V 18-12 passage the said length Y equals an lper 531,201X X 2 References Cited by the Applicant 3 Z (Z 1 UNITED STATES PATENTS2,734,224 2/1956 Winstead. where b equals the depth of the rearrestrictive 2 813 301 11/1957 Underwooi passage, L is one-half the totaltransverse width 2 901 9/1959 Beck of the passage and C is a constantfunction of the geometry of the supply chamber. OTHER REFERENCES 2. Anextrusion die according to claim 1 Where the 25 M d Pl ti page 112, July1960, chamber area forming the restricted passage is of lesser depththan the chamber area of the cross-flow chamber. WILLIAM J. STEPHENSON,Primary Examiner.

1. AN EXTRUSION DIE FOR CONTROLLING THE FLOW OF FLUID ALONG DIVERGINGPATHS FROM AN INLET TO AN THROUGH A NARROW SLOT OUTLET COMPRISING: (A) ABODY MEMBER HAVING AT LEAST ONE INLET AND AN OUTLET TERMINATING IN ASIDE SURFACE OF THE BODY MEMBER, A PORTION OF SAID SURFACE DEFINING ONESURFACE OF THE SLOT OUTET. (B) A FLUID CONTROL PLATE ON A SIDE SURFACE,THE INNER SURFACE OF WHICH PLATE HAS A SERIES OF INTERCONNECTEDDEPRESSED CHAMBER AREAS FORMING WITH SAID SIDE SURFACE (1) A CENTRALLYDISPOSED INLET AREA, (2) AN NOBSTRUCTED TRANSVERSE SUPPLY CHAMBER, (3) ATRANSVERSE UNOBSTRUCTRED REAR PASSAGE, AND (4) AN UNOBSTRUCTED SECONDTRANSVERSE CROSS-FLOW CHAMBER THAT PROVIDES ANOTHER FLOW CONTROL PASSAGEADJACENT THE SLOT OUTLET AND COMMUNICATES WITH SAID SLOT OUTLET, THELENGTH OF THE TRANSVERSE REAR RESTRICTED PASSAGE IN THE DIRECTION OFFLUID FLOW FROM SAID CENTRALLY DISPOSED INLET AREA TO THE SLOT OUTLETBEING VARIED ALONG DIVERGING PATHS